Sidor then turned his attention to trying to hack an Android phone so it would take photos without its owner knowing.

Every attempt he made failed in one way or the other - the phone wouldn't let him do it, or it would show a big preview screen, which is certainly a tipoff.

Finally, Sidor hacked the preview screen itself, making it 1 pixel by 1 pixel - about the size of the period at the end of this sentence.

The result was amazing and scary at the same time - the pixel is virtually impossible to spot on Nexus 5 screen (even when you know where to look)! Also it turned out that even if you turn the screen completely off, you can still take photos, as long as the pixel is still there.